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What is Computer Memory?

Memory is the sum total of what we remember.

It gives us the capability to learn and adapt
from previous experiences as well as to build relationships. It is the ability to remember past
experiences and the power or process of recalling to mind previously learned facts,
impressions, skills and habits. It is the store of things learned and retained from our activity
or experience, as evidenced by modification of structure or behaviour or by recall and recognition.As memory is necessary for our happy existence, memory is an essential element of a
computer. Without its memory, a computer is of hardly any use. Memory plays an important
role in saving and retrieving data. The performance of the computer system depends upon
the size of the memory.

Categories of Memory

There are two categories of memory in a computer, they are –

1. Volatile Memory
2. Non-Volatile Memory

Volatile Memory- Volatile Memory losses all the content stored in it when the computer is switch off.

Non-Volatile Memory – Non-volatile Memory does not lose all its content stored in it when the computer is switched off.

REPRESENTATION OF MEMORY

The memory is represented with characters. Let us read about the various terms related to memory.

Byte

A byte is the smallest group of information that a computer can process in one chunk or
bite. The bits in a byte are processed together, and more importantly the byte is presented
to us in a form that we can understand. Each byte can be encoded to correspond to a digit,
a letter of the alphabet, a punctuation character or other symbols.

Kilobyte 👉 1024 characters are equal to one kilobyte.
Megabyte. 👉 1,048,576 characters are equal to one megabyte.
Gigabyte 👉 1,073,741,824 characters are equal to one gigabyte.
Terabyte 👉 1,099,511,627,776 characters are equal to one terabyte.

 

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TYPES OF MEMORY

The memory of computer is divided into two types,namely:
👉Primary Memory (RAM, ROM)
👉Secondary Memory (Floppy Disk, CD-ROM, Hard disk)

Primary Memory

Primary storage unit is used for four activities Input/Output operations; Manipulations of text and calculation operation; Logic/Comparison operation; Storage and retrieval operations. Primary memory is the memory which is used to store the currently running program and the data being processed and their results. This is generally a temporary
storage area. It is used when small amount of data have to be exchanged quickly and used repeatedly. It is a very fast memory but is of small storage capacity. Examples of primary
memory are RAM, ROM, Cache Memory, etc.

Types of Primary Memory

👉 RAM (Random Access Memory).

👉 ROM ( Read Only Memory)

RAM

RAM stands for Random Access Memory and is the most common type of memory used in
computers. A Computer’s RAM is the memory used to store data and programs on a
temporary basis. The RAM is compared to short-term memory, as it stores applications
and information that is actively used while the system is running. In comparison, the hard
drive stores all programs and information permanently, whether the computer is
powered on or not. The amount of RAM directly affects a computer’s performance. The more RAM a computer has, the more programs and documents it can have open without
slowing the system down. Current PC computers have anywhere from 256 MB of RAM or
256 million bytes of memory a program can use, to as much as 4 GB of RAM. Mac Computers generally have between 128 and 512 MB of RAM.

Some common types of RAM are as follow :

SRAM

It is used primarily to create CPU’s speed-sensitive cache. Static Random Access Memory(SRAM) uses multiple transistors for each memory cell. It does not have a capacitor in each
cell.

 

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DRAM

Dynamic Random Access Memory needs to be refreshed consistently and contains
memory cells with a paired transistor. In order to activate the transistor at each bit in the column, DRAM sends a charge through the appropriate column (CAS).
The level of charge is determined by the sense-amplitier while reading. If the level of charge exceeds fifty percent, it is read as 1, whereas if the charge is below fifty percent, it is read as 0. For dynamic memory to work, either the CPU or the memory controller recharges all the capacitors before they are discharged to zero.

SDRAM

Synchronous Dynamic Random Access Memory enhances the system’s performance by
utilizing the burst mode concept. With maximum transfer rate to L2 cache of 528 mbps,

SDRAM

stays on the row that contains the requested bit and moves quickly through the columns to read each bit as it moves on. FPM DRAMThe pristine form of DRAM, Fast Page Mode Dynamic Random Access Memory waits through the process of locating a bit of data by column and row and then reading the bit and then starts on the next bit. It has a maximum transfer rate to L2 cache of about 176mbps.

EDO DRAM

Contrary to FPM DRAM, Extended Data-Out Dynamic Random Access Memory does not
wait and as the address of the first bit is located, it starts looking for the next bit. With
maximum transfer rate to L2 cache of about 264 mbps, it is 5 percent faster than the FPM.

RDRAM

Rambus Dynamic Random Access Memory uses a special high speed data bus called the
Rambus Channel. It generates more heat than other chips as they operate at high speeds.

DDR SDRAM

Double Data Rate Synchronous Dynamic Random Access Memory is somewhat similar to
SDRAM but has higher bandwidth. It has a maximum transfer rate to L2 cache of about 1064 mbps

ROM

Read Only Memory (ROM) is an integrated circuit programmed with data that holds instructions for starting up the computer. Data stored in ROM is non-volatile and is not
lost when powered off. These data cannot be changed or a special operation is needed to be performed to change it.A ROM chip cannot be reprogrammed or rewritten, therefore, when the chip is created, it requires the programming of perfect and complete information. ROM chips are cost effective and use very little power.

Some common types of ROM are as follow:

SPROM

Programmable Read Only Memory (PROM) is a type of ROM. These chips are non-volatile and cannot be purged to store something else once it has been used. Blank PROM chips can be coded with the help of a tool known as a programmer. Similar to ROM, PROM chips also have a grid of rows and columns, but here fuses connect the intersections.

EPROM

Erasable Programmable Read Only Memory can be erased with the help of ultraviolet light and rewritten many times. These chips are configured by the EPROM programmer, providing the voltage at the specified levels.
The floating gate is linked to the row through the control gate. The cell has a value of 1 till the link remains established. A process known
as Fowler-Nordheim tunneling is pertormed to change the value to zero.

EEPROM

Electrically Erasable Programmable Read
Only Memory chips are not required to be removed to be erased or rewritten. These chips do not require to be erased altogether and specific portion of it can be easily altered.
Additional dedicated equipment are also not required to change the content of the FEPROM chips. These chips are erased and rewritten with the help of electric charge.

Cache Memory

The Cache Memory is the memory which is very nearest to the CPU. All the recent instructions are stored into the Cache Memory. The Cache Memory is attached for storing the input which is given by the user and which is necessary for the CPU to perform a task.But the capacity of the Cache Memory is too low in comparison to Hard Disk.

The cache memory lies in the path between the processor and the memory. The cache memory, therefore, has lesser access time than memory and is faster than the main,st memory. A cache memory has an access time of 100ns, while the main memory may have an access time of 700ns.

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Secondary Memory

This is also called Mass Storage, Auxiliary Memory and External Memory. This memory is slower than them main memory as it involves mechanical motion techniques during
storage and retrieval of data. This memory is larger in size than main memory but the processor is unable to access it directly due to its offline link with the processor. This means that the data from secondary storage must be loaded into RAM before the processor
starts processing it. The main memory links the secondary memory to the processor.

Types of Secondary Memory

Magnetic Tape

Magnetic tape has been in use for more than 50 years.
Modern magnetic tape is packaged in cartridges or cassettes and is used for storing data backups, particularly in corporate settings. The average amount of storage is 5 MB to 140 MB for every standard-length reel, which is
2,400 feet.

Hard Disk

Hard Disk is a thin circular metallic plate coated on both sides with a magnetic oxide material. It is a non-removable storage device. A set of such magnetic plates is fixed to a spindle one below the other to make up a disk pack. Each circular division of disk surtace is known as track. Verticulor horizontal division of a disk surtace is called as sector.

Floppy Disk

Floppy disks are a storage medium made of a thin magnetic disk. They were widely used from the 1970s to the early 2000s. On the 3-inch micro floppy, common from the late 1980s  Onwards, storage capabilities ranged from the
standard 1.44 MB to 200 MB on some versions.

CD-ROM

CD-ROM, a type of recordable CD, is an optical secondary storage device invented by Sony and Philips. It is also known as a WORM – Write Once Read Many Medium.

DVD-ROM

DVD-ROM, a type of recordable DVD, has a storage capacity of usually 4.1 GB. There is also an 8.54-GB dual-layer version, called DVD-R DL.

USB Drive

USB Flash Drive, usually portable and re-writable, is a type of flash memory storage device that plugs into
a computer’s USB port. Flash drives are more expensive than hard drives with the same storage capacity.

 

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